Hitherto, as a photographic support, polyethylene terephthalate, cellulose triacetate, polystyrene, polycarbonate, polyolefin laminated papers, etc., have frequently been used owing to the excellent transparency, flexibility, etc.
However, in the case of using such polymers as the support, it has been very difficult to strongly adhere a photographic layer composed of a hydrophilic colloid comprised mainly of gelatin to the support, since the support has a hydrophobic surface. For overcoming such difficulty, the following surface treatment methods of the hydrophobic support have hitherto been practiced:
(1) Methods involving a surface activation treatment such as a chemical treatment, a mechanical treatment, a corona discharging treatment, a flame treatment, an ultraviolet treatment, a high frequency wave treatment, a glow discharging treatment, an active plasma treatment, a laser treatment, a mixed acid treatment, an ozone oxidation treatment, etc., have been applied to the surface of the support, followed by coating directly thereon a photographic emulsion, whereby good adhesion is obtained, and
(2) Methods involving applying a surface activation treatment as above-described to the surface to the support, then forming a subbing layer thereon, and thereafter coating a photographic emulsion layer on the subbing layer.
Such methods are described, for example, in U.S. Pat. Nos. 2,698,241; 2,764,520; 2,864,755; 3,143,421; 3,462,335; 3,475,193 and 3,615,556; U.K. Patent Nos. 788,365; 804,005; 891,469, etc. Among the above-described methods, methods of type (2) are more effective and widely employed.
It is considered that in these surface treatments, the adhesive power of the surface is increased due to polar groups, more or less, being formed on the surface of the support, which is originally hydrophobic; a thin layer giving negative effect for the adhesion of the polar surface is removed; the crosslinkage density on the surface of the support is increased to increase the bonding strength, etc. It is also considered that as a result of the above effect, the affinity with the polar groups of the components contained in the coating composition for the subbing layer is increased, and the fastness of the adhered surface is also increased.
Also, various attempts have been practiced as a method of coating a subbing layer on a support. For example, there are a so-called double layer method wherein a layer adhering well to a support is formed as a first layer, and then a hydrophilic resin layer is formed thereon as a second layer, and a single layer method wherein only one resin layer containing both a hydrophobic group and a hydrophilic group is formed on a support by coating.
These methods have been well investigated. For example, the aptitudes of copolymers formed using a monomer selected from vinyl chloride, vinylidene chloride, butadiene, methacrylic acid, acrylic acid, itaconic acid, maleic anhydride, etc., and various resins such as polyethyleneimine, epoxy resin-grafted gelatin, nirtocellulose, etc., have been investigated as is disclosed in U.S. Pat. Nos. 3,501,301, 3,271,178.
In particular, for performing a subbing method of obtaining a sufficient adhesive power capable of enduring practical use between a hydrophobic support and a hydrophilic silver halide emulsion in a complete aqueous system, a vinylidene chloride copolymer and a dienic copolymer has been investigated.
As a method of adhering a support and a silver halide emulsion layer, the inventors previously found that a copolymer containing a dienic monomer as a component is effective for a coating composition of a subbing layer solely or with a proper crosslinking agent as described, for example, In Japanese Patent Application (OPI) Nos. 114,12/76; 94,025/79 and 65,949/80 (The term "OPI" as used herein refers to a "published unexamined Japanese Patent Application").
It is thus well known that a hydrophilic material such as gelatin or a gelatin derivative is coated on a base support having a subbing layer for obtaining a good adhesive power with a photographic emulsion layer. In such cases if the support is allowed to stand in a state such that the subbing layers are in contact with each other, a so-called "blocking phenomenon" is liable to occur, and this tendency is particularly remarkable under high humidity and high pressure. As a method of preventing the occurrence of the blocking phenomenon, there is a method of coating a subbing layer on a support, and coating further, before winding the support, a second subbing layer composed of gelatin containing a hardening agent such as formaldehyde, etc., or a matting agent, and then winding the support. Also as a method of preventing the occurrence of blocking without using the second subbing solution, there is a method described in Japanese Patent Application (OPI) No. 119,919/'77 wherein the thickness of the subbing layer is limited to arange of from 0.25 to 1.0 micron, and synthetic polymer particles having a mean particle size of from 0.1 to 10.0 microns and a glass transition temperature of higher than 45.degree. C. are incorporated in the layer as a type of matting agent.
However, these methods have the following various disadvantages. First, the film loses its transparency to some extent, which also reduces the quality of the photographic product. Second, in the steps from drying to winding of the support after coating thereon a subbing layer containing a matting agent, and in the steps of coating the support with a photographic hydrophilic organic colloid layer such as a silver halide photographic emulsion layer to winding of the photographic film, the matting agent is transferred onto rolls which are brought into contact with the support. Third, during coating and drying of the subbing layer, the matting agent existing in the subbing solution forms nuclei and makes heterogeneous the properties of the subbing solution, such as surface tension, etc., which results in causing pin hole-like foam or stains, thus reduce the commercial value as a photographic film support. Fourth, when photographic films thus prepared are stored under high humidity (higher than 60% RH) and high pressure (higher than 1 kg/cm.sup.2), a sufficient blocking prevention effect is not obtained. These disadvantages occur by the presence of the matting agent in both the cases of a single layer coating and a double layer coating.
As a method of not using a matting agent, there is a method of incorporating a hardening agent in the second layer, but this method also has disadvantages, since the photographic properties are significantly influenced by the kind and amount of the hardening agent incorporated in the layer, the adhesion with a silver halide emulsion layer (which is the original purpose of a subbing layer) becomes insufficient, and the blocking prevention effect is insufficient. Thus, such method is not effective for practical purposes.